I have a hunch you might have used too much of Mary Ellen's Best Press. Starch is thicker and as a result it doesn't saturate fabric as fast as Mary Ellen's.
I use it all the time and I make sure to use just a little squirt. I've thought of using a brush to apply it to an edge before sewing the ¼" seam. I'm cheap...I don't always want the entire area stiffened..might be a mistake but it has worked for me so far. Sometimes I just want the two pieces to stay in place with more than my usual "steam pin" technique.